function show_hide() {
        if(document.getElementById("dn2").style.display!='block') {
			document.getElementById("dn").style.display = 'none';
            document.getElementById("dn2").style.display = 'block';
        }
        else {
			document.getElementById("dn").style.display = 'block';
            document.getElementById("dn2").style.display = 'none';
        }
        return false;
    }
$(document).ready(function(){
		$("#tutorial").submit(function(){
					var name        = $('#name').attr('value');
					var email       = $('#email').attr('value');
					$.ajax({
						type: "POST", 
						url: "./libs/xulydangnhap.php", 
						data: "name="+ name +"&email="+ email,
						success: function(answer){$('#FormDK').html(answer);}
					});
					return false;
			});
		});
<!-- full BG -->
$(window).load(function() {    
	var theWindow        = $(window),
	    $bg              = $("#bg"),
	    aspectRatio      = $bg.width() / $bg.height();	
	function resizeBg() {
		if ( (theWindow.width() / theWindow.height()) < aspectRatio ) {
		    $bg
		    	.removeClass()
		    	.addClass('bgheight');
		} else {
		    $bg
		    	.removeClass()
		    	.addClass('bgwidth');
		}		
	}	                   			
	theWindow.resize(resizeBg).trigger("resize");
});
<!--end full BG -->